Sulfite Is Not Required for N2 Reduction Catalyzed by Mo-Nitrogenase
Zhi-Yong Yang1, Dmitriy A Lukoyanov2, Ana Pérez-González3
1Department of Chemistry and Biochemistry, Utah State University, Logan, Utah 84322, United States.
Journal of the American Chemical Society
|April 17, 2026
Summary
Sulfite is not required for Mo-nitrogenase to convert nitrogen (N2) into ammonia (NH3). Studies show the enzyme functions effectively without sulfite, both in vitro and in vivo, challenging previous hypotheses.
Area of Science:
- Biochemistry
- Enzymology
- Nitrogen Fixation
Background:
- Mo-nitrogenase catalyzes N2 to NH3 conversion via the FeMo-cofactor.
- A recent hypothesis proposed sulfite is essential for NH3 release and cofactor regeneration.
Purpose of the Study:
- To investigate the necessity of sulfite in Mo-nitrogenase activity.
- To test the hypothesis that sulfite is required for N2 reduction and cofactor regeneration.
Main Methods:
- Turnover studies of Mo-nitrogenase under sulfite-free conditions.
- Using reduced viologen as a reductant and preparing proteins without dithionite or sulfite.
- Electron paramagnetic resonance (EPR) spectroscopy analysis.
- Assessing diazotrophic growth in *Azotobacter vinelandii*.
Main Results:
- Mo-nitrogenase efficiently catalyzed N2 and proton reduction without sulfite.
- Steady-state turnover and H2-formed/N2-reduced ratios were comparable to dithionite-supported reactions.
- EPR confirmed FeMo-cofactor regeneration in the absence of sulfite.
- *Azotobacter vinelandii* growth was unaffected by bypassing sulfite formation.
Conclusions:
- Sulfite is not required for Mo-nitrogenase-catalyzed N2 reduction.
- The enzyme functions effectively both *in vitro* and *in vivo* without sulfite.
- This finding refutes the proposed essential role of sulfite in the catalytic cycle.
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